Walleye Fingerling Culture in Undrainable Ponds

Transcription

1 Kinnunen, R. E Walleye fingerling culture in undrainable ponds. Pages in R. C. Summerfelt, editor, Walleye culture manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Walleye Fingerling Culture in Undrainable Ponds Ronald E. Kinnunen, Michigan State University - Upper Peninsula, 702 Chippewa Square, Marquette, Michigan Introduction To obtain control over the pond production process and to facilitate harvest of walleyes, many agencies use drainable ponds, however, the natural resource agencies in Michigan and Minnesota still rely heavily on the use of undrainable ponds for walleye fingerling culture. Some pond management procedures, such as fertilization and control of predaceous insects and nuisance aquatic plants, are similar for both drainable and undrainable ponds. The major differences between the two culture systems is in harvest methods. In undrainable ponds, active seining or trap nets are used. Also, in undrainable ponds which do not winterkill, fish carryover is avoided by treatment with a piscicide (e.g., rotenone). In the production phase from fry to fingerling, walleye first rely exclusively on zooplankton then benthc organisms, and finally they become piscivorous, at which time they must be harvested or provided with suitable prey (minnows). Fertilization and stocking rates cannot be defined to raise a specific sized fish. Walleye fingerling production is variable, and sitespecific factors account for much of this variation. Summerfelt et al. (1993) reported that procedures to culture walleye fry to a desirable sized fingerling in earthen ponds have not been standardized, and culture methods are site specific. Factors such as soil type, water fertility, and stocking levels influence the abundance and composition of zooplankton populations in ways that are unpredictable walleye producers in Minnesota use natural ponds that are 5-10 ft ( m) deep, which are deep enough to prevent summerlull but shallow enough to winterlull. These ponds are typically 5-30 acres ( ha) but can range from acres ( ha). Daily (1996) inhcated that Minnesota Department of Natural Resources prefers to use ponds larger than 50 acres (20.2 ha), but they also use ponds that are less than 5 acres (2 ha) and some that are larger than 100 acres (40.5 ha). They prefer ponds with depths up to 15 ft (4.6 m) to prevent summerkill. Low fertility ponds that do not winterkill and are less than 5 acres (2 ha) are usually avoided. Lilienthal(l987) reported that statecontrolled walleye culture ponds in Minnesota averaged 58 acres (23.5 ha) while statewide cooperative walleye culture ponds averaged 27 acres (1 0.9 ha). Michigan Department of Natural Resources Fisheries Division, uses walleye culture ponds (Figure 1) that a, Pond selection The case studies on walleye culture in undrainable ponds show variability in criteria for pond selection. Gunderson et al. (1996) reported that commercial Figure 1. An undrainable walleye culture pond in Michigan. 3 C c Y c i? + > 0? 0 0 NCRAC Culture Series Walleye Culture Manual 135

2 range from acres ( ha) in size (Gustafson 1996). Laarman and Reynolds (1 974) indicated that undrainable walleye culture ponds in Michigan should be a minimum of 5 acres (2 ha) with a maximum depth of 6-8 ft ( m) and minimal shallow areas less than 3 ft (0.9 m) to discourage aquatic weed growth. Table 1. Oils used to control predacious aquatic insects in walleye culture ponds. Application Rate Oi I g a Wac re Uha Reference Fuel Oil Gunderson et al. (1996) Gustafson (1996), Laarman and Reynolds (1974) Buttner (1989) Richard and Hynes (1986) Ke rose ne Gunderson et al. (1996) Fish Oil Gunderson et al. (1996) Vegetable Oil Buttner (1 989) Water quality #-i bunderson et al. (1996) reported that private walleye producers in Minnesota generally use ponds with alkalinities of ppm, but alkalinity ranges from ppm. The ph in these ponds ranged from The dissolved oxygen typically was 5-10 ppm. Gustafson (1996) indicated there was a large variation in alkalinity, ph, and productivity in walleye culture ponds used by the Michigan Department of Natural Resources. Summerfelt et al. (1993) found that when dissolved oxygen levels in walleye culture ponds dropped below 3 ppm, the addtion of water and aeration should be used. Richard and Hynes (1986) and Laarman and Reynolds (1 974) indicated that dissolved oxygen was the most important water quality parameter, and should be at least 5 pprn at dawn. Buttner (1989) recommends that dissolved oxygen and temperature measurements be taken daily at dawn, and turbidity, ph, ammonia-nitrogen, nitrate-nitrogen, and phosphate be measured twice each week. Aquatic pest control Aquatic insect control Predaceous aquatic insects are often controlled by oil application. A variety of oils have been used to control air-breathing aquatic insects in walleye culture ponds (Table 1). Gunderson (1996) suggested that these oil applications be made on the windward side of the pond under moderate wind conditions. Such applications should be avoided within 2 weeks prior to stocking walleye fry or within 3 weeks after stocking (Gustafson Alkalinity levels below 40 ppm and ph levels below 6.5 or above 9.0 are not suitable for walleye culture (Richard and Hynes 1986) They further indicated that the optimum temperature for walleye fingerlings is "F (21- Table 2. Rotenone applications to eradicate the fish populations in ponds. This is usually done in undrainable ponds to eliminate fish populations before walleye are stocked. Rotenone is a restricted use pesticide and applied only in accordance with state and federal guidelines. In many states this would require certification as an aquatic pesticide applicator. Contact State Department of Agriculture. 22"C), although temperatures greater than 86 F (30 C) may be Rate Ref ere nce tolerated for a short period of time. Laarman and Reynolds (1 974) indcated that temperatures above 85 F (29.5"C) are detrimental. 1 gal/acre-foot (3.8 Uacre-foot) Daily (1 996), Lilienthal (1 989) 2 pprn (2.5% synergized liquid formulation) Jorgensen (1996) 1-4 ppm Buttner (1989) 136 NCRAC Culture Series 101- Walleye Culture Manual

3 1996). Summerfelt (personal communication) indicated that using oils to control insects within 2 weeks of stocking walleye fry or within 3 weeks after stocking may prevent gas bladder inflation. Before using any oil, the user should insure that any federal, state, or local laws do not restrict its use. Fish contrul To control unwanted fish in walleye culture ponds, a piscicide (e.g., rotenone) is applied; usually this is immediately after fall harvest (Table 2). Obtain a copy of the label before purchasing or using any commercial product to make sure the product is approved for its intended use. A number of restrictions may apply to use some compounds. Restricted-use products such as rotenone fish toxicants can be purchased only by a Certified Pesticide Applicator or under a certified applicator s direct supervision (Federal Joint Subcommittee on Aquaculture 1994). Look for the restricted use pesticide designation on the label to identify such products. Before using any chemical, the user should insure that any federal, state, or local laws do not restrict its use. Temperature, light, oxygen, and alkalinity affect the breakdown rate of rotenone. Rotenone used in 80 F water will detoxify in less than 4 days, while at 45 F the toxicity to fish may last for 33 days. In waters that are acihc, very soft, or deep and stratified detoxification of rotenone may take longer. At temperatures above 60 F, most waters treated with rotenone completely detoxify within 5 weeks of treatment. Other factors that influence the degradation rate of rotenone and reduce its toxic effect include the presence of organic debris, turbidity, pond shape and depth, and dilution by inflowing water. Ice and snow cover may prolong the toxic effect of rotenone. Aquatic plant control Specific chemicals have been used to control aquatic plants in walleye culture ponds (Table 3). Caution should be used as concentrations of copper products can be toxic to fish, especially in soft water. Some of these chemicals can only be used if there is no discharge into public waters. It is the responsibility of the user to always refer to the product label for details on recommended or approved treatment rates and usages as well as for any restrictions on use. Gustafson (1 996) reported that mechanical harvesting of algae and macrophytes has been successful in clearing areas for fingerling harvesting, but it is labor intensive. Table 3. Chemicals used to control aquatic plants in walleye culture ponds. Use of chemicals is regulated by the EPA and FDA. They may be used only in accordance with state and federal guidelines. Contact State Department of Agriculture. In many states this would require certification as an aquatic pesticide applicator. Aquatic Plant Chemical Rate Reference Macrophytes Aq uazi n etm 1 Jorgensen (1 996) Potamogeton Copper sulfate 0.5 ppm Summerfelt (1993) Summerfelt (1993) Aq uazi n etm ppm Chara Copper sulfate Aq uazi n etm ppm 2.2 ppm Summerfelt (1993) Summerfelt (1993) Hydrodicton Copper sulfate 0.4 ppm Summerfelt (1993) Laarman and Reynolds (1974) Laarman and Reynolds (1974) Summerfelt (1993) Copper sulfate Copper sulfate Aq uazi n etm ppm (alkalinity >50 ppm) 0.25 ppm (alkalinity 4 0 ppm) 1.7 ppm Not available, no longer registered for aquatic applications. NCRAC Culture Series Walleye Culture Manual 137

4 Fert i I izat ion and Zoo plankton Gunderson et al. (1996) reported that the use of fertilizers among Minnesota private walleye producers is a matter of experience and varies from pond to pond. Zooplankton are, at times, seeded before fry are stocked and later when a decline is detected. Zooplankton are monitored by towing a plankton net ft ( m) through the pond early in the morning or late evening. Daily (1 996) indicated that Minnesota Department of Natural Resources does not use artificial fertilization on their walleye culture ponds because it is not practical or economical for ponds of the size that they use (58 acre average). The productivity of each of their ponds is influenced by alkalinity, ph, depth, nutrient load, and fish species present. Large amphipod populations were found to be important, and if amplvpods were not present they could be inoculated. Their policy is to rest the less fertile ponds on a regular basis, especially those under 30 acres (1 2.1 ha). No sampling or monitoring of their ponds is done throughout the summer. Michigan Department of N at ur a1 Resources Fisheries Division uses an initial application of fertilizer two weeks prior to fry stocking, when ponds are fertilized. Fertilizers are then applied as needed. Fertilizers include grain by-products, animal manure, yeast, inorganic fertilizer, hay, or a combination of these. Monitoring of zooplankton abundance (Figure 2) and composition is initiated before fry are stocked and twice per week thereafter, and inoculation of zooplankton is done as needed (Gustafson 1996). Buttner and Kirby (1 986) found that walleyes ate mainly cladoceran, copepods, and chironomid larvae and pupae. When compared with their abundance in the zooplankton, rotifers were found in significantly lower and chironomids, cladocerans, and copepods in significantly greater proportions in walleye stomachs. Westers (1 980) indicated that a key to successful pond culture of walleye is to maintain a 10: 1 weight ratio of food organisms to fish. Dobie (1 956) was the first to note a relationship between fertility of pond substrate and walleye production. In ponds with less than 4% organic matter in the soil, aquatic insects are scarce and walleye fingerlings are often lost to cannibalism when a zooplankton shortage develops. Ponds with soils of a high organic content usually produce more fish in natural ponds than in drainable ponds where water is changed every year, The goals of pond culture are to produce large crops of microcrustaceans, such as cladocerans and copepods, in the spring to ensure good fry survival and microcrustaceans and insects, such as cluronomids, to feed the fish in midsummer (Laarman and Reynolds 1974; Richard and Hynes 1986; Buttner 1989). Enrichment of walleye culture ponds is attained by using organic or inorganic fertilizers. Richard and Hynes (1 986) indicated that organic fertilizers play a greater role in benthic development than inorganic fertilizers, which have not been commonly used for walleye culture. Bacteria and protozoans growing in decomposing organic fertilizers are consumed by certain zooplankton. Figure 2. Zooplankton are monitored by towing a plankton net through the pond. Inorganic fertilizers appear to be more practical in ponds with soils of low fertility (Laarman and Reynolds 1974). However, chances for increased filamentous algae growth is greater using inorganic fertilizer as release of nutrients into water is more rapid when compared with organic fertilizer. Buttner (1989) reported that 138 NCRAC Culture Series 101- Walleye Culture Manual

5 inorganic fertilizers have performed inconsistently, and frequently promote poor water quality and should be used cautiously. Such fertilizers should only be used if nitrogen and/or phosphorus is deficient. Compared with inorganic fertilizers, the rate of release of nitrogen and phosphorus into the water is slower with organic fertilizers (Dobie 1971). Culver et al. (1993) stated that it was difficult to adjust the relative amounts of nitrogen and phosphorus added to ponds with organic fertilizers, such as alfalfa meal. They found that the ad&tion of small amounts of inorganic fertilizer each week avoided the production of filamentous algae. Inoculation of walleye culture ponds with zooplankton should occur immediately after ice melts and at least 2-3 weeks before fry are stocked (Buttner 1989). Richard and Hynes (1986) recommended inoculating the center of walleye culture ponds with zooplankton at organisms/gal ( organismsl) at the beginning of the culture season or when zooplankton populations abruptly decline ( crash ). Monitoring zooplankton populations in walleye culture ponds should occur on a regular basis, and fertilizer application schedules can then be adjusted to encourage zooplankton blooms (Summerfelt 1 993). Zooplankton monitoring can be accomplished through weekly plankton tows, using an 80 mm plankton net and separating the sample into Copepoda and Cladocera (Richard and Hynes 1986). Hardmg and Summerfelt (1993) collected zooplankton samples at night, using a flexible impeller pump and 80 mm plankton net, through which the pond water was filtered. Buttner (1 989) determined zooplankton abundance 2-3 times per week, using a flashlight after sunset and collecting them as they congregated near the light. An undesirable situation would include few microcrustaceans and cladocerans with incubating ephippia (resting stages) rather than eggs/larvae. If presunrise concentration of dissolved oxygen is less than 4 ppm, the midday ph is greater than 9, total ammonia is >1 ppm, then fertilization is excessive and should be reduced, and supplemental aeration or addition of water may be necessary (Buttner 1989). If zooplankton abundance is decreasing or if the composition is shifting to less desirable taxa (i.e., rotifers, which are poorly utilized by walleye) and water quality is acceptable, then the fertilization rate may be increased and the pond can be inoculated with ad&tional zooplankton. Walleye stocking densities, fertilization rates, and yield The stochng density of walleye fry and the ultimate yield of walleye fingerlings will depend on basic pond fertility. Pond fertility can be controlled through intensive management with the use of fertilizers. Table 4 summarizes various management practices presented in the case studes. Stocking The stocking density of walleye fry will vary, depending on basic pond fertility and whether aeration is used. In Minnesota private walleye fingerling producers typically stock 2,500-10,000 fry/acre (6,180-24,710 fryha), but 20,000-30,000 fry/acre (49,420-74,130 fry/ ha) are stocked if the pond or lake is aerated, more intensively managed, or known to be very productive (Gunderson et al. 1996). Minnesota Department of Natural Resources walleye culture program found that early efforts to stock fry at 10,000-50,000 fry/acre (24, ,550 fryha) met with limited success. Typically, stocking densities now range from 3, ,000/acre (7,410-24,710ha) (Daily 1996). Michigan Department of Natural Resources determines walleye fry stocking rates on past pond performance, relative productivity, and harvest plans. Typically stocking rates are 30,000-75,000 fry/acre (74, ,325 fryha). To determine growth and survival, samples of fish are collected at night 3 and 6 d after stoclung using a light and fine-mesh aquarium net, thereafter, monitoring is every two weeks. Fingerlings are collected with a small-mesh seine (Gustafson 1996). At Spirit Lake Fish Hatchery, Iowa, fry are stocked at 20,000 fry/acre (49,420 fryha). Fish are monitored weekly after they are 2-3 weeks old (Jorgensen 1996). Attempts to define an ideal stocking density is pointless as water productivity levels, pond configuration, and organic soil content vary, ensuring carrying capacity will also vary (Richard and Hynes 1986). In drainable ponds, Harding and Summerfelt (1993) reported that NCRAC Culture Series Walleye Culture Manual 139

6 Table 4. Summary of stocking rate, fertilization, survival, and yield for the four case studies of walleye culture in undrainable ponds. Stocking Rate (f ry/ac re) Fertilization S u rv iva I ( /) Fish size at harvest Case Study Ref ere n ce 2, ,000 20,000-30,000 30, ,000 10,000-50,000 3, ,000 20,000 Varies by pond Intensively managed Intensively managed 30 None Poor None None in (July) 4-8 in 15-25/1b (SepVOct) 2-3 in (July) 4-8 in 15-25/1b (SepVOct) in (4-8 wks) Gustafson (1996) - Daily (1996) 25.6/1 b in (first cropping) in (second cropping with fathead minnows) Gunderson (1 996) Jorgensen (1 996) stocking density ranged from 1 1, ,820/acre (29, ,000/ha). Laarrnan and Reynolds (1 974) recommend stoclung densities of 50,000-75,000/acre (123, ,325/ha). Richard and Hynes (1986) inhcated that realistic stocking densities are 25,000-30,000 walleye fry/acreft, but higher densities can be used in extremely productive waters. They further found that stocking densities whch are too high can lead to competition for food resources which will stunt growth, while lower stoclung density can lead to less competition and maximize the quality of fish produced. Summerfelt et al. (1 993) stocked walleye fry at lol,175/acre (250,000ha) in unfertilized, drainable ponds and noted that zooplankton such as copepods, cladocerans, and rotifers were present at densities of 500-2,500/L during the production period. Chironomid larvae were abundant in the pond substrate. Fertilized drainable ponds were stocked at 15lY ,452/acre (375, ,000/ha). Stockmg 182,115 fry/acre (450,000 fry/ha) in ponds fertilized with inorganic fertilizer appeared appropriate for obtaining both the greatest total numbers and yield (Culver et al. 1993). Fertilization Buttner (1 989) used grain by-products, such as finely ground wheat sorts, alfalfa meal, or soybean meal applied at lbs/acre ( kg/ha) with half applied immediately after ice-out, before fry are stocked. An application of lbs/acre ( kg/ha) is done every 7-10 d to maintain zooplankton. Fertilization with yeast at lbs/acre ( kg/ha) can be applied concurrently with the grain byproducts. Beyerle (1979) found that weekly applications of sheep or horse manure, plus Torula or brewer s yeast, stimulated the production of Daphnia which was the first and main food of walleye. Applications of hay, sewage sludge, or sucrose as substitutes for the manure-yeast combination failed to stimulate adequate Daphnia populations. Peterson (1973) added 3.5 bales of hay/ acre (8.6/ha) in unproductive borrow pits in Michigan in the fall prior to ice formation. The following spring, weekly applications of 30 lb/acre (33.6 kg/ha) of Torula yeast began two weeks prior to stoclung. After stoclung, yeast was applied bi-weekly. Successful walleye production in Minnesota was obtained by delaying the application of yeast about one month after stocking, especially in ponds with greater organic matter in bottom soils. Richard and Hynes (1986) fertilized ponds with fermented soybean meal at 99 lb/acre-ft/week (45 kg/ 140 NCRAC Culture Series 101- Walleye Culture Manual

7 acre-ftfweek) beginning two weeks prior to stocking. Application continued throughout the 6- to 8-week culture period and was terminated 1 week before harvest or if dissolved oxygen levels dropped or the amount of algae and macrophytes increase dramatically. Dobie (1971) found that fertilization with dried sheep manure to provide 2.4 lb (1.1 kg) of nitrogen per 1,000 m3 and weekly applications of brewer s yeast at 100 lb/ acre (1 12 kg/ha) starting when cladoceran populations declined produced the best seasonal distribution of zooplankton and benthic organisms. Summerfelt et at. (1993) fertilized drainable ponds with a total of 714 lb/acre (800 kg/ha) of alfalfa pellets applied in four weekly applications during the culture period. Fertilizer application was managed to prevent excessive algae blooms. Other drainable ponds were fertilized with 357 lb/acre (400 kgha) of ground alfalfa hay applied weekly during the culture period in four equal applications for a total of 1,428 lb/acre (1,600 kg/ ha). Chironomids averaged nearly 3,000/m2 in week one to nearly 8,000/m2 in week four. Culver et al. (1993) developed inorganic fertilizer regimens for drainable ponds in Oho, that increased fingerling yield 4-fold. Optimal inorganic fertilization was identified as that needed to restore nutrient levels to 600 mg NLL (NH+ NO) and 30 mg P/L as PO? weekly. They found that alkalinity, ph, and temperature are factors that could potentially influence its adoption at other sites. Weekly chemical analysis and fertilization requires more time, but discontinuing the use of alfalfa hay and meal has, in turn, decreased labor and material costs. Yield Generally, Minnesota farmers obtain a % survival to fingerling stage, but it may reach 30-40%. Some of the fingerlings are harvested in early July when they are 2-3 in (50-76 mm); most are harvested in September and October when they are 4-8 in ( mm) or 15-25Ab (33-55kg). Conservative estimates are that 600,000 walleye fingerlings were produced in 1992 by Minnesota fish farmers (Gunderson et al. 1996). There is a negative relationship between average harvest size at harvest and stochng density when stocking rates exceed 5,000/acre (12,350ha). In 1993, Minnesota Department of Natural Resources had an average statewide production of 2.4 million walleye fingerlings from over 240 natural ponds. These ponds produced 21 8 fingerlingdacre (540 fingerlingdha) and survival averaged over 3.2%. In other years it ranged from 10-50%. Between 1982 and 1986, the average yearly production was 3.6 million fingerlings, which was 25.6 fish/lb (56 fish/kg) (Daily 1996). Michigan Department of Natural Resources operates over 100 walleye culture ponds statewide, and in 1990 over 5.7 million fingerlings were produced. The production season lasts 4-8 weeks and fish are harvested before the zooplankton crashes when they are in (38-63 mm). Production averaged 7,000 walleye fingerlingdacre (1 7,300/ha); survival was 30% (Gustafson 1996). The Iowa Department of Natural Resosurces uses two harvests from Welch Lake. The first cropping occurs at a rate of 1,370 fingerlingdacre (3,385 fingerlingsha) when fingerlings reach in (50-64 mm). Fathead minnow are then stocked and the walleye are harvested in September when they reach 5-6 in ( mm); at that time harvest rates are 1,930 fish/acre (4,770 fish/ ha) (Jorgensen 1996). Beyerle (1979) used a stocking density of 3.5 fry/m3 which produced fish that averaged 50 mm in 6-7 weeks; survival rates were >90%. Lilienthal (1989) found that stockmg rates of 5,000/acre (12,35O/ha) in unfertilized non-drainable productive ponds have the capability of producing 10 lb/acre (1 1.2 kg/ha), with survival of 5-7.5%. Larger ponds produced larger fingerlings. There was a negative relationship between the average harvest size when stocking rates exceeded 5,00O/acre (12,350ha). Therefore, walleye stocking rates should not be less than 3,00O/acre (7,410ha) or more than 10,00O/acre (24,71O/ha) (Lilienthal 1987). Laarman and Reynolds (1 974) indicated that production goals should be 6, ,000 of in ( cm) fingerlingdacre (40-50 lbs, kg). Buttner (1989) developed walleye culture methods that averaged 50% survival of fry stocked at 20,00O/acre (49,42O/ha). Fingerlings reached in (40-60 mm) d after stochng in unfertilized drainable ponds (Summerfelt et al. 1993). Fingerlings reached 1.3 in (32 mm) d after stocking, and yield was NCRAC Culture Series Walleye Culture Manual 141

8 lb/acre ( kgha); survival ranged from % in fertilized drainable ponds (Summerfelt et al j. In other drainable fertilized ponds fingerling yield averaged lb/acre ( kg/ha) and survival ranged from %. Harding and Summerfelt (1993) stocked drainable ponds at lol,175/acre (250,000iha); ponds were either unfertilized or fertilized with four weekly applications of either alfalfa pellets at 189 lb/acre (212 kg/ha) for a total of 757 lb/acre (848 kg/ha) or soybean meal at 79 lb/acre (88 kgha) for a total of 314 lb/acre (352 kg/ha). No significant dfference in yield, number of fingerlings harvested, mean length, and mean weight were observed. They then stocked fry at 101,175 and 15 1,762/ acre (250,000 and 375,00O/ha) into ponds which were either unfertilized or fertilized with alfalfa pellets at 126 lb/acre (141 kgha) applied in six weekly applications for a total of 757 lb/acre (848 kg/ha). Yield was greater in fertilized ponds at both stochng densities. Fingerlings with the largest average weight were raised in fertilized ponds stocked at 101,175/acre (250,000/ha), while the smallest fingerlings were from unfertilized ponds stocked at 15 l,762/acre (375,000/ha). Survival averaged 64.7% and d d not dffer between density treatments. NCRAC (1994) research in drainable ponds in Nebraska demonstrated that the number of walleye fingerlings that can be produced per acre can be increased 2-3 times above present levels without affecting survival and with only a small reduction in size. The success of this approach depended on harvesting fingerlings when they were in (34-44 mrnj and before the forage base collapsed and water temperatures became a problem. In one experiment, survival (71-81%) and fish size at harvest ( in, mm) was similar for ponds stocked at 163,904 and 245,653 fry/acre (405,000 and 607,000 fry/ha) and fertilized weekly with 134 or 201 lb/acre (1 50 or 225 kg/ha) of alfalfa pellets supplemented with phosphoric acid. In a second experiment, ponds were stocked at 163,904, 245,855 and 324,003 fry/acre (405,000, 607,500 and 800,600 fry/ha), but all ponds received the same weekly application of alfalfa pellets (303 lb/acre, 340 kg/ha) and liquid phosphoric acid. At harvest, the fish stocked at the lower density were significantly longer and heavier than those stocked at the lugher densities. However, neither stoclung rate nor aeration had an affect on survival (69-79%) or yield lb/ acre ( kgha). Culver et al. (1 993 j found that doubling the initial stocking density increased harvest from 60, ,410 fishlacre (150, ,000 fishha) and increased yield from lb/acre ( kg/ha) when using inorganic fertilizer in drainable ponds. Forage fish introductions Pkivate producers in Minnesota often stock fathead minnows 4.5 in (<38 mm) as forage fish when walleye reach 2-3 in (50-76 mm) (Gunderson et al. 1996). In contrast, Minnesota Department of Natural Resources discourages this practice because of the extra labor and expense to purchase minnows (Daily 1996). To produce 3-6 in ( mm) fingerlings, the Michigan Department of Natural Resources Fisheries Division thn walleye densities and then stock fathead minnows (Gustafson 1996). At the Welch Lake production site of the Spirit Lake Fish Hatchery, Iowa, the population of walleye fingerlings is partially harvested with seines when the fish reach in (50-63 mm), then the lake is stocked with 2,816 fathead minnowdacre (6,958ha) on a weekly schedule thereafter (28,016/acre or 69,230/ ha total) until harvest of fall fingerlings 5-6 in ( cm) (Jorgensen 1996). Laarman and Reynolds (1974) question the value of addmg forage fish. Adult fathead minnow and brook stickleback have been responsible for low survival of walleyes because of interspecific competition (Beyerle 1979 j. Ponds with dense fathead minnow populations severely depress zooplankton densities and adversely affect walleye survival (Lilienthal 1989; Daily 1996). Cannibalism Richard and Hynes (1986) reported that cannibalism can occur within a 6-8 week culture period if zooplankton populations collapse. They suggested that maximum walleye fingerling production may be attained by periodcally removing the larger cannibalistic fingerlings. Smith and Moyle (1945) observed that fingerlings may become cannibalistic at 1 in (25 mm); however, when there is an abundance of zooplankton, fingerlings were in (76-89 rnmj before switching to a fish diet. After walleye fingerlings reach 1.57 in (4.0 cm) 142 NCRAC Culture Series 101- Walleye Culture Manual

9 survival diminishes quickly because of cannibalism, unless there is an abundance of largesize zooplankters (Westers 1980). A decision must be made about whether greater mortality will occur from cannibalism or from increased handling of the fish during thinning operations. Some culturists think that adding forage fish prevents cannibalism, while others offer reasons to suggest that once walleye begin a piscivorous lifestyle, cannibalism w ill increase. Harvest techniques Although some fingerlings are harvested in early July when they are 2-3 in (50-76 mm), most commercial walleye producers in Minnesota harvest fish when they are 4-8 in ( cm) or 15-25/lb (33-35kg) in September and October when water temperatures are <60"F (<15.6"C) (Gunderson et al. 1996). Seining is used when conditions permit (Figure 3), but in most undrainable ponds trap netting is the only practical method for harvest. In the early 1970's, switching from seining to trap netting with the use of copper sulfate in natural ponds helped remove limitations on the use of large ponds (Lilienthal 1989). Trap nets are set along the shoreline at intervals of yd ( m). Figure 3. Seining walleye in an undrainable pond. Fingerlings trapped using ths technique were usually in excellent condition. Culturists at Spirit Lake Fish Hatchery, Iowa, use seines to harvest fingerlings (Jorgensen 1996). Seines 1,000 ft (305 m) long with V-in (6-mm) mesh are used to remove in (50-63-mm) fingerlings, while seines 2,800 ft (853 m) long with 'bin (12-mm) mesh are Michigan Department of Natural Resources harvests fingerlings 4-8 weeks after stocking, when fish reach in (38-63 mm). Fingerlings are harvested with the use of l/e1/4-in (3-6-mm) mesh fyke nets (Figure 4) which are 4 X 4 ft (1.2 x 1.2 m) and 6 ft (1.8 m); lead lengths depend on the pond (Gustafson 1996). Copper sulfate ( ppm) is used to stimulate fish movement in the pond to increase trapping rates. Figure 4. Fyke nets like these are used to harvest walleye fingerlings in undrainable ponds. NCRAC Culture Series Walleye Culture Manual 143

10 used to remove 5-6-in ( mm) walleye. Gunderson et al. (1996) reported that large ponds are difficult to harvest, so the returns are less when compared with smaller ponds. If fingerlings are uniform in size, fyke nets '/x-in (9- mm) mesh can be used to harvest fish that weigh 45/lb (99kg). Lilienthal(l987, 1989) recommended applying copper sulfate at no less than 0.5 Ib/acre-foot (0.56 kg/ ha-foot) in ponds with a ph 4.5. In ponds with total alkalinity >150 ppm and water temperatures >48"F (>9OC) copper sulfate should be applied at 1 lbhcrefoot (0.37 ppm). Applications occur when few fish are netted after the first lift or after catches have declined. Richard and Hynes (1 986) recommended using 6 minifyke netshrface acre (1 5 mini-fyke nets/ha) with green or red colored mesh to harvest walleye fingerlings. Copper sulfate was added at a rate of 4-6 lb/surface acre ( kgha) to irritate fish and which encouraged them to swim more actively. It should be noted that although copper sulfate is an EPA-registered algicide, it is not registered as a fish irritant to increase the movement of fish. Richard and Hynes (1986) reported that improper harvesting methods can kill fingerlings, especially when the water temperature is >77"F (>25"C). Harvest usually occurs when fingerlings reach in (50-60 mm), when zooplankton populations diminish, or when cannibalism or emaciation of fish occurs. Seines usually have 0.25-in (6-mm) mesh for fish between 1.5 and 2.5 in (38 to 63 mm), but larger mesh (0.5 in, 12 mm) is used for 5 to 6 in ( mm) walleye. Seining continues until the number of remaining fish is negligible. Peterson (1973) used 0.25-in (6- mm) mesh nylon seines 150 ft (46 m) long and 12 ft (3.6 m) deep. Buttner (1989) recommended seining early in the morning to harvest in (35-65-mm) fingerlings. Climate influence on pond culture Cold and cloudy weather during the first 2-3 weeks of culture, can prevent an adequate zooplankton bloom which will cause massive mortality as fish have no source of food (Richard and Hynes 1986). Periods of unusually cold weather temporarily inhibit zooplankton production and reduce walleye growth and survival (Beyerle 1979; Westers 1980). Summerfelt et al. (1993) found greater year-to-year variations in yield and survival than pond-to-pond variation within years which suggests climatic factors strongly influence production. They also noted that differences in the mean water temperature affected the length of the culture period, with higher mean temperatures resulting in shorter culture periods to grow fish to the same size. References Beyerle, G. B Extensive culture of walleye fry in ponds at the Wolf Lake Hatchery, Michigan Department of Natural Resources Research Report 1874, Lansing, Michigan. Buttner, J. K Culture of fingerling walleye in earthen ponds-state of the art Aquaculture Magazine 15(2): Buttner, J. K., and J. Kirby Response of zooplankton and walleye fry to cladoceran inoculation and fertilization of earthen ponds. New York Fish and Game Journal 33: Culver, D. A., S. P. Madon, and J. Qin Percid pond production techniques: timing, enrichment, and stocking density manipulation. Journal of Applied Aquaculture 2:9-31. Daily, J Pond culture of fingerlings in undrainable ponds. Pages in R.C. Summetfelt, editor. Walleye Culture Manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Dobie, J Walleye pond management in Minnesota. Progressive Fish-Culturist 17: Dobie, J Minnesota walleye nursery ponds and transportation of fingerling walleye. Pages in Proceedings of North Central Warmwater Fish Culture-Management Workshop. Iowa Cooperative Fishery Unit, Iowa State University, Ames, Iowa. Federal Joint Subcommittee on Aquaculture, Guide to drug, vaccine, and pesticide use in aquaculture. Texas Agricultural Extension Service, The Texas A & M University System, College Station, Texas. Gunderson, J., P. Goeden, T. Hertz Walleye fingerling culture in undrainable, natural ponds. Pages in R.C. Summetfelt, editor. Walleye 144 NCRAC Culture Series 101- Walleye Culture Manual

11 Culture Manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Gustafson, C Pond culture of walleye in Michi- gan: fry to advanced fingerling. Pages in R.C. Summerfelt, editor. Walleye Culture Manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Harding, L. M., and R. C. Summerfelt Effects of fertilization and of fry stocking density on pond production of fingerling wall eye, Stizostedion vitreum. Journal of Applied Aquaculture Jorgensen, W. D Extensive culture of walleye fingerlings. Pages in R.C. Summerfelt, editor. Walleye Culture Manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Laarman, P. W., and D. E. Reynolds Methods for propagation of walleye fingerling in Michigan. Technical Report 74-5, Michigan Department of Natural Resources Fish Division, Lansing, Michigan. Lilienthal, J Walleye production. Minnesota Department of Natural Resources, St. Paul, Minne- sota. Lilienthal, J Natural walleye rearing ponds. Minnesota Department of Natural Resources, St. Paul, Minnesota. NCRAC North Central Regional Aquaculture Center annual progress report. Michigan State University, East Lansing, Michigan. Peterson, J. H Rearing of walleye in the Moss Lake and Rapid River borrow pits. Technical Report 73-30, Michigan Department of Natural Resources Fish Division, Lansing, Michigan. Richard, P. D., and J. Hynes Walleye culture manual. Ontario Ministry of Natural Resources, Fish Culture Section, Toronto, Ontario. Smith, L. L., and J. 6. Moyle Factors influencing production of yellow pikeperch, Stizostedion vitreum vitreum, in Minnesota rearing ponds. Transactions of the American Fisheries Society 73(1943): Summerfelt, R. C., C. I? Clouse, L. M. Harding Pond production of fingerling walleye, Sfizostedion vitreum, in the Northern Great Plains. Journal of Applied Aquaculture 2: Westers, H Extensive pond rearing of walleyes. Michigan Department of Natural Resources, Lansing, Michigan. NCRAC Culture Series Walleye Culture Manual 145

12 146 NCRAC Culture Series 101- Walleye Culture Manual

13 Daily, J Pond culture of fingerlings in undrainable ponds. Pages in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Pond Culture of Fingerlings in Undrainable Ponds John B. Uailx 3501 Louisiana Ave. N. Apt. 220 Crystal, MN Introduction walleye is one of the most desired sport fishes by Minnesota anglers. The Minnesota Department of Natural Resources (DNR) has stocked walleye fry and fingerlings in lakes that have insufficient recruitment to sustain a walleye fishery. To meet the demand for fingerlings, artificial propagation has been practiced in this state for almost 60 years in both drainable and natural ponds. Early efforts in drainable ponds consisted primarily of evaluating fry stocking densities, but results with stocking fry at 10,000 to 50,000 fry/acre (24, ,550/ha) were inconsistent. This problem led to research to provide guidelines that would enable consistent levels of fish harvest. Experience inhcated that stocking ponds with 3,000-5,000 fry/acre (7,413-12,355ha) would be sufficient stocking densities when the goal was to obtain a fall-fingerling that would weigh 30Ab (66kg) or larger. Large fall fingerlings were needed to avoid high mortality of stocked fish. Evaluation of the contribution of stocked walleye to walleye populations in state lakes indicates that stocked fish only contribute to year-class strength in a lake when the stocked fish are of a size to compete successfully with the resident population of walleye for the young-of-theyear yellow perch, their preferred prey. In 1993, the DNR operated 13 seasonal hatcheries which are located from the southwest part to the northeast. These hatcheries obtain most of their walleye eggs from broodstock collected from natural river-runs of walleye. Most collection sites are located in the northwest and central parts of the state. In 1993 over 2.4 million fingerlings were stocked into state waters. Over 240 natural ponds are operated by state personnel. Since 1990, production levels have been decreasing by deleting stocking from lakes where stocking was not needed or ineffective. Pond selection During the 1960 s, many DNR area managers began using natural ponds and small lakes that winterkilled on an annual or semiannual basis. Most ponds were on pubic lands, some were leased from private land owners, and other ponds were also available under a cooperative program with various sportsmen groups and local lake associations. In the early years of walleye culture, there was a lack of information about proper pond size, and depth, watershed factors, and management strategies. Ponds ranged in size from less than five acres to more than one hundred acres. The major constraint was an inability to harvest fingerlings using seines. Seining was not effective in ponds with tree stumps or heavy stands of submergent vegetation. In the early 1970 s, the major harvest method changed from seining to trap netting which allowed the use of ponds that could not be seined. Because of the large geographic range of the ponds over the state of Minnesota, there was a large variation in alkalinity, ph, depth, nutrient load, fish fauna, and yield. In the 1980s, fish managers learned more about proper pond management and the impact of chemical and biological condtions. Today ponds are only used when they meet the following criteria: 1. There must be an annual winterkill of all the fish. 2. Water depth (up to 15 ft, 4.5 m) should be sufficient to avoid surnmerkill and to have a temperature strata that allows the young walleye to avoid high summer temperatures. 3. Ponds in forested areas are avoided because of natural low fertility. 4. Ponds must be >5 acres (>12.4 ha) but less than 100 acres (247 ha), a range of 50 to 100 acres ( ha) is better, and the ideal size is >50 acres (124 ha). 5. The pond should be accessible to trucks and have a suitable site to launch a boat from which nets can be set and fish harvested. Other factors considered in pond selection are potential conflict among user groups, wildlife concerns, and bait producers. It seems that walleye production triggers considerable public interest and controversy because of NCRAC Culture Series Walleye Culture Manual 147

14 Chapter 6 -Walleye Fingerling Culture in Undrainable Ponds perceived conflicts in DNR Wildlife management areas, Federal Waterfowl production areas (WPAs), or when there will be competition with private aquaculture. Production data Ponds are classified as cooperation ponds and statecontrolled ponds. Cooperative ponds represent about 15% of the pond acreage and 25% of the ponds by number. In 1984, the average size of these ponds were 27 acres (66.72 ha) compared to 58 acres (143.3 ha) for state-controlled ponds. Between 1982 and 1986 the average statewide production averaged 3,634,000 fingerlingdyear, with an average size of 25.6 fish/lb (56.4 fish kg). Pond management It is important to have a hydrographc map for each pond. Water chemistry should be monitored. Dissolved oxygen, ph, and total alkalinity are the most essential variables. In February and early March oxygen levels will determine whether winterkill was effective to prevent carryover of fish. Carryover of walleye fingerlings will result in a &minished production capability for the coming year. Ponds can be sampled with trap nets with 0.25-in (6.4-mm) mesh nets a few weeks after ice-out to determine if any fish survived. Plankton populations should be assessed along with bottom soil types and shoreline depths. Ponds with large stands of emergent vegetation are avoided because they will make fish harvest difficult. Amphpod ( scuds ) populations Gammarus Zacustris (up to 22 mm) and HyaZeZZa azteca (up to 8 mm) should be assessed, as they provide important forage for the fish. Gammarus is the largest and most important of these scuds; they only survive in waters with a total alkalinity over 80 ppm. A pond that lacks Gummarus, but meets the alkalinity criteria can be inoculated with Gummarus by adding at least a 0.5 lbs/acre (0.56 kg/ha). Fertility appears to be a variable that greatly effects production, but artificial fertilization is not considered practical. Yield declines sharply in the third year of continued production. For this reason, some less fertile ponds are rested on a regular basis, especially so when they are <30 acres (74 ha). Numerous pond checks during the summer are not usually required, but a check prior to harvest helps determine the mesh size needed for the trap net, and harvest priority can be set, generally, ponds with larger fish are first to give ponds with smaller fish an opportunity to grow. To provide consistency in pond production detailed records should be kept. Pond stocking Fry stocking rates should not exceed more than 5,000/ acre (12,355/ha) to obtain fall fingerlings that will average 25-3O/lb (55-66kg). There seems to be a negative (inverse) relationship between average size of walleye fingerling harvested and stochng density. Stocking rates in excess of 5,000 per surface acre (12,355/ha) will not produce fingerling fish that reach the desired size. When fry are planted at (~5,000 fry/ surface acre, (12,355ha) can usually produce a quality size fingerling (larger than 30/lb, 66kg) in small ponds (larger than 50 acres, ha) for lake stoclung. Pond reclamation Pond reclamation (i.e., treatment with rotenone to kill all fish) may be needed in natural ponds, but ths is prohibited for ponds >lo0 acres, (247 ha). Reclamation is done only on an exceptional basis on ponds less than 100 acres (247 ha), when large numbers of black bullheads and common carp are present. Abundant populations of fathead minnows, dace, and or sticklebacks can reduce fry survival even though such populations would be desirable forage for larger fish. Typically, walleye culture in ponds that have other fish present are usually a failure. Restricted-use products such as rotenone fish toxicants can be purchased only by a Certified Pesticide Applicator or under a certified applicator s hrect supervision (Federal Joint Subcommittee on Aquaculture 1994). Look for the restricted use pesticide designation on the label to identify such products. Before using any chemical, the user should insure that any federal, state, or local laws do not restrict its use. Rotenone treatments are best done in the late fall rather than in the spring. When treated in the fall the zooplankton has time to recover, and become abundant the following spring before fry are stocked. Ponds that are free of competitors and predators greatly improve harvest and lowers the handling stress on walleye fingerlings. Inoculation with preferred zooplankton and scuds in the spring is also desirable. In the past, minnows have been stocked as forage, but present stuhes indxate that this practice is inefficient and is a 148 NCRAC Culture Series 101- Walleye Culture Manual

15 Walleye Fingerling Culture in Undrainable Ponds - Chapter 6 costly method to increase average size. Fathead minnows can compete with larval walleye for food. Conclusion The Minnesota Department of Natural Resources walleye culture program has produced fingerlings for stocking reclaimed lakes, maintenance stocking, and introduction to waters without walleye (e.g. winterkill lakes and bass-panfish lakes). Minnesota has around 1 million acres of walleye water to manage. This program of extensive production in natural ponds began in the 1930s. Ponds used for walleye culture are found throughout the state and are managed by 6 regional offices and 22 of 28 area stations. An average of all ponds in statewide production produced 21 8 finger- lingdsurface acre (538ha) in 1993 with a fingerling average return of 3.2%. Generally ponds have averaged from 10 to as high as 50% return from fry stocked. There is great diversity in physical, chemical, and geographical characteristics of these ponds. Each pond must be managed on an individual basis thus there is no single recipe for success. Nutrient levels, nuisance plants, predatory insect populations, and established fish populations all provide some limitations as to production success. Harvest methods have been modified to accommodate pond types by bottom content, size, and available work force. The method of harvest are practiced on a pond by pond basis. Even with the best possible management scheme the harvest success is largely dependent on weather. NCRAC Culture Series Walleye Culture Manual 149

16 Chapter 6 -Walleye Fingerling Culture in Undrainable Ponds 150 NCRAC Culture Series 101- Walleye Culture Manual

17 Jorgensen, W. D Extensive culture of walleye fingerlings. Pages in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. Extensive Culture of Walleye Fingerlings Wallace D. Jorgensen, Spirit Lake Fish Hatchery, nd Avenue, Spirit Lake, IA Introduction The information presented in this case study describes the methods used at Spirit Lake State Fish Hatchery to raise fingerling walleye in Welch Lake, a shallow winterkill lake located in northwestern Iowa (Figure 1). Culture in other nursery lakes is quite similar to this lake. Two harvest are made from Welch lake, first 2 to 2.5 in (5.1 to 6.4 cm) fingerlings are harvested in June to thin the population to obtain fish for tank culture and for stocking, This harvest reduces population density and fathead minnows are added to provide forage to raise the remaining fingerlings to about 6-in (15.2 cm). Methods welch Lake is a 57-acre (23 ha) glacial lake with an average depth of 5.1 ft (1.6 m). Total alkalinity averages 176 ppm. Daytime ph ranges from 8.2 to 9.0. Because carryover of walleye from one season to the next would result in predation by yearling fish on the newly stocked fry, in late October the lake is treated with 2 ppm rotenone to kill all fish. In the past, the pond was treated in early spring with Aquazine at 2 ppm to prevent a vegetation problem in June when the first harvest is made. procedure has not been compared with other methods to enumerate fry, we find it expedient for stocking large numbers of walleye fry. We subtract the number of fry removed from the catch tanks against the number of eyed eggs remaining in the incubators to maintain our inventory of eyed-eggs. Zooplankton (cladoceran and copepod) populations in Welch Lake are monitored using a fine mesh plankton net. A heavy planktonic bloom usually occurs during the first week in May at about the time fry are stocked. First harvest Weekly sampling of fish is started when fish are 2-3 weeks old to gain awareness of fry survival and growth rate. The first harvest is started when fish have reached a size of 2 to 2.5 in ( cm) total length (400 to 210/lb, kg). Fish are captured with a 1,000 ft, %-in (6.3 mm) mesh seine. At this time, about 78,000 fish are seined and transported to the hatchery for training to formulated feed and for stocking. Fish are Counting fry The lake is stocked with 2-day old fry at about 20,00O/acre (49,420/ ha). Fry for stocking are estimated by the visual comparison method whereby an unknown fry density is compared with a counted sample. Fry density in a plastic bag with a known quantity of water is compared to a counted population of fry in the same volume of water. A periodic check is made to confirm that the comparison method is giving a reasonable estimate. Although the accuracy of this Figure 1. Welch Lake (foreground), a shallow winterkill lake in northwest Iowa that is used by the Iowa Department of Natural Resources to raise walleye fingerlings. NCRAC Culture Series Walleye Culture Manual 151

18 Chapter 6 -Walleye Fingerling Culture in Undrainable Ponds transported from the lake to the hatchery building in a tank truck using pure oxygen to maintain oxygen levels. A saline solution is added to the water to reduce physiological stress. The saline solution is composed of 4.3 lb (1.95 kg) sodium chloride, 0.17 lbs (80 g) potassium chloride, lb (50 g) monopotassium phosphate, and 0.09 lb (40 g) magnesium sulfate per 100 gal (378 L) water. Addition of forage fish After the first harvest, population monitoring is continued weekly. When walleye reach 185 fish/lb (407/kg) about 1,600 lbs (726 kg) of fathead minnow are introduced as forage (28 lb/acre, 31.4 kg/ha). Thereafter, fathead minnows are stocked weekly (1 8 lb to 25 Ib/acre, 20.2 to 28 kgha), depending on walleye growth and abundance of forage. We typically use about 16,000 lb (727 kg) of minnows for the growing season (281 lbs/acre, 315 kgha), which represents about 3 lb (1.4 kg) of minnows for each pound (0.45 kg) of advanced fingerlings that are harvested. However, to avoid overstoclung minnows, forage stoclung is adjusted to the abundance of walleye fingerlings. Second harvest The second harvest occurs in early October when fingerlings are about 5 to 6 in ( cm). Fingerlings are harvested using a 1/2-in (12.7 mm) bar measure mesh drag seine, 2,800 Et (853 m) long. With one or two hauls per day, it takes 5-6 d to harvest most of the fingerlings. Fish are transported as described earlier. Production costs Expenses for manpower, chemicals and vehicle uses are similar each year, consequently, variation in production numbers affect fingerling costs each year. Production may range from less than 110,000 to 350,000 walleyes annually. A normal production year would yield 78,000 (260 Ib) of 2 to 2.5 in (5-6.4 cm) and 110,000 (5,789 lb) 5 to 6 in ( cm) fingerlings. The total harvest (188,000 fingerlings) is 16.5% of the fry stocked. Yield is 106 lbs/ acre ( kg/ha). Production costs are about $51.OO/thousand (5.1 q!) for 2.5 in (6.3 cm) fish and $253.00/thousand (25.3G) for 5 to 6 in ( cm) fingerlings. Figure 2. Five to six in (12.7 to 15.4 cm) walleye fingerlings obtained from the second (fall) interval. In most years extensive lake culture is a satisfactory way to produce fingerlings, however, one of the major drawbacks is the unpredictable number of fish that can be produced. Fry must be stocked within 5-days posthatch, but cold weather and other factors may reduce zooplankton populations causing a sharp reduction in survival. 152 NCRAC Culture Series 101- Walleye Culture Manual